Have no fear. I found this OG calculator; you can put in your ingredients and procedures and it gives a decent estimate for OG, FG, IBU, ABV, and what sex your next child will be: http://beercalculus.hopville.com/recipe
I've tried it and compared it to my hydrometer readings; let me know if any of you have used this and had mixed results.
tasty brew has one of those calcultors too. i did the same thing with my first batch.i was worried about bottle bombs cuz i got a hydro right before botteling it was 1.016 and thats exactly what the FG came out to not saying yours will be exact and i dont believe all grain are going to be 100% exact either. those calculators have extract and partial mash settings for type of boil.its up to the yeast to decide when its done. an estimate then consecutive readings that dont drop anymore
You are going to run into accuracy problems doing extract and PM batches with those calculators. You have 2 different efficiencies going on. Yours with the grains and the Malter's efficiency with the extract. It will be close but not exact.
Those calculators work best for AG brewers who know their efficiency.